Among solid carbon materials, nanocarbon materials in which all atomic positions can be located have recently drawn great attention since they were discovered to have characteristics including specifically high electron mobility at room temperature, very low electric resistance at room temperature, and high thermal conductivity.
The nanocarbon materials are divided in terms of their structure into fullerene, carbon nanotubes, and graphene. With respect to graphene, for example, a method for producing graphene by effecting high-temperature heat treatment on a silicon carbide (SiC) substrate in vacuum, for letting silicon atoms sublime from the surface of the silicon carbide substrate, whereby the remaining carbon atoms form graphene on the surface of the silicon carbide substrate was proposed (JP-A 2007-335532 (Patent Document 1)).
This method, however, has such problems as the necessity of heat treatment of very expensive silicon carbide substrates at extremely high temperature, and difficult working of silicon carbide substrates. For mass scale production, a number of expensive silicon carbide substrates must be furnished. From both the aspects of production process and price, the method is quite difficult to implement.
Also, a method of producing graphene by heat treating a silicon carbide substrate to form a graphene film, bonding the silicon carbide substrate to a support substrate (other than silicon carbide substrate) such as silicon substrate or quartz substrate, followed by separation was proposed (JP-A 2009-200177 (Patent Document 2)).
This method, however, has such problems as extreme difficulty to separate the graphene film having an atomic layer thickness from the silicon carbide substrate and very low production yields.
To solve the outstanding problems, a method of producing graphene by growing a silicon carbide layer on a silicon substrate or silicon film, and laser heating the layer to convert its surface into a graphene film was proposed (JP-A 2012-31011 (Patent Document 3)).
However, when silicon carbide is grown on a silicon substrate or silicon film, the resulting silicon carbide film contains many defects since strains are induced in the crystal structure. This gives rise to the problem that the graphene film also contains many defects.
Also, a method of producing a graphene film by epitaxially growing a silicon carbide layer and letting silicon atoms sublime is proposed, but has the drawback of many defects.
On the other hand, a method of simply forming a graphene sheet utilizing a metal catalyst such as nickel is proposed (JP-A 2009-91174 (Patent Document 4)).
On use of the metal catalyst, however, a catalyst metal layer having high electrical conductivity is left behind, which inhibits to design a functional electronic device using the graphene film alone.